Recently, the performance and functionality of digital cameras and digital movie cameras that use some solid-state image sensor such as a CCD and a CMOS (which will be simply referred to herein as an “image sensor”) have been enhanced to an astonishing degree. In particular, the size of a pixel structure for use in an image sensor has been further reduced these days thanks to rapid development of semiconductor device processing technologies, thus getting an even greater number of pixels and drivers integrated together in an image sensor. And the performance of image sensors has been further enhanced as well. Meanwhile, cameras that use a backside illumination type image sensor, which receives incoming light on its back surface side, not on its principal surface side with a wiring layer for the solid-state image sensor, have been developed just recently and their property has attracted a lot of attention these days. Nevertheless, the greater the number of pixels in an image sensor, the lower the intensity of the light falling on a single pixel and the lower the sensitivity of cameras tends to be.
The sensitivity of cameras has dropped recently due to not only such a significant increase in resolution but also the use of a color-separating color filter itself. In an ordinary color camera, a subtractive color filter that uses an organic pigment as a dye is arranged to face each photosensitive cell of an image sensor. A color filter transmits one color component of incoming light to use but absorbs the other components of the light. That is why with such a color filter, the optical efficiency of a camera would decrease. Specifically, in a color camera that uses a Bayer color filter arrangement in which color filters in three colors are arranged using a combination of one red (R) pixel, two green (G) pixels and one blue (B) pixel as a fundamental unit, the R color filter transmits an R ray but absorbs G and B rays, the G color filter transmits a G ray but absorbs R and B rays, and the B color filter transmits a B ray but absorbs R and G rays. Consequently, the sum of the quantities of light that can be used by a color camera with the Bayer arrangement is approximately only one-third of the entire incoming light. Thus, the use of a color filter would cause a decrease in the optical efficiency and the sensitivity of those cameras.
Thus, to overcome such a problem, Patent Document No. 1 discloses a color representation technique for increasing the optical efficiency by using a dispersing element which splits the incoming light according to its wavelength instead of the color filter. According to such a technique, a dispersing element which is arranged to face its associated photosensitive cell makes light rays incident on multiple different photosensitive cells according to their wavelength ranges. Each of those photosensitive cells receives light in which components falling within multiple different wavelength ranges are superposed one upon the other from a plurality of dispersing elements. As a result, a color signal can be generated by performing a signal arithmetic operation using photoelectrically converted signals supplied from the respective photosensitive cells.
Meanwhile, Patent Document No. 2 discloses a color representation technique in which a dispersing element is applied to an image sensor with an oblique pixel arrangement (i.e., a so-called “honeycomb arrangement”). According to such a technique, the optical efficiency can be increased as much as in Patent Document No. 1.